Hydrocracking is a catalytic process which has achieved widespread use in petroleum refining for converting various heavy petroleum fractions into lighter fractions and more valuable products, especially gasolines, jet fuels, diesel oils, heating oils and lubes oils.
In a typical hydrocracking process, the petroleum feedstock is brought into contact with a catalyst at temperatures in the range of about 250.degree. C. to about 430.degree. C., hydrogen pressure in the range of about 200 to about 2000 psi, and space velocity in the range of about 0.5 to about 2.5 h.sup.-1.
The catalysts are all of the bifunctional type, combining an acid function with a hydrogenating-dehydrogenation function. The acid function is provided by catalytic support of relatively large surface area (about 150 to 600 m.sup.2 /g) having a specific surface acidity, such as halogenated alumina, amorphous silica alumina and zeolite. The hydrogenating-dehydrogenation function is provided either by one or several metals of Group VIII of the Period Table of Elements in the sulfided or reduced state, such as palladium, ruthenium or platinum, or by a combination of at least two or more metals chosen from Group VIB of the Periodic Table of Elements, such as molybdenum or tungsten in particular, and Group VIII of the Periodic Table of Elements such as cobalt or nickel. At least two of the metals of such a combination belong to two different Groups (Group VI and Group VIII as previously mentioned), and in order of preference, NiO--WO.sub.3, NiO--MoO.sub.3, CoO--Mo.sub.3 and CoO--Wo.sub.3.
The conventional catalysts in catalytic hydrocracking are mostly moderately acidic substrates, such as silica-alumina, a combination of boron or titania, and fluorinated aluminum oxides or phosphates of alumina. These catalytic systems are often used to produce very good quality middle distillates, or oil bases. Many hydrocracking catalysts on the market consist of silica-alumina combined with the aforementioned metals of Groups VIB and VIII of the Periodic Table of Elements. These catalyst systems have very good middle distillate selectivity. The products formed are of good quality. These catalysts can also produce lubricating bases. The disadvantage of all these catalyst systems, all based on an amorphous catalyst support, is their low activity, however.
Acid zeolites, on the other hand, have the advantage over the other previously mentioned acidic substrates of providing a much higher degree of acidity. Hydrocracking catalysts which contain such zeolites are therefore much more active, and for that reason permit relatively lower process temperature and/or a higher feed space velocity. The higher acidity modifies the equilibrium between the cracking and hydrogenating catalytic functions, respectively. Zeolite-based hydrocracking catalysts have a relatively higher cracking capability, and therefore produce more yield in gasolines, jet fuels and/or middle distillates than conventional ones.
In order to obtain specific products, considerable effort has been made to develop and commercialize highly active and selective catalysts for hydroconversion of heavy distillation fractions and residue into middle distillates, jet fuels and lube oils and for deep hydrogenation of aromatic compounds contained in these fractions.
For example, U.S. Pat. No. 5,229,347 to Prada et al. describes mild hydrocracking and deep hydrogenation of aromatics with a catalyst comprising nickel, tungsten, and ruthenium or palladium on a co-precipitated support of alumina-titania. The support is prepared from solution of aluminum sulfate, titanyl chloride (TiOCl.sub.2), and sodium aluminate. Titania in the support constitutes more than 5 wt-%. Catalytic metals are then impregnated onto the support following one or more sequential impregnation steps.
U.S. Pat. No. 5,009,768 to Galiasso et al. describes a hydrocracking process that requires two or more hydrotreatment stages followed by hydrocracking using a catalyst bed of a particular composition for the mild hydrocracking stage.
U.S. Pat. No. 4,855,530 to LaPierre et al. describes a process for isomerizing relatively long chain paraffins. The catalyst used in the described process is a large pore zeolite such as a Y-type zeolite, beta-type zeolite, or ZSM-20 zeolite.
U.S. Pat. No. 4,797,195 to Kukes et al. discloses three reaction zones in series in a hydrocracking process which comprises: a first reaction zone where the hydrocarbon feedstock with hydrogen is contacted with a nickel-molybdenum support on alumina catalyst, a second reaction zone where the effluent from the first reaction zone is contacted with a nickel-tungsten deposited on a support consisting of an alumina component and a crystalline molecular sieve, specifically a Y-type zeolite, and a third reaction zone where the effluent from the second reaction zone is contacted with a catalyst comprising a cobalt-molybdenum system deposited on a support component comprising a silica-alumina and a crystalline molecular sieve component, specifically a Y-type zeolite.
U.S. Pat. No. 4,495,061 to Mayer et al. discloses a hydrocarbon conversion process using a particular catalyst in connection with petroleum distillates and solvent--deasphalted residual feeds containing nitrogen impurities at levels below about 10 ppmw to produce high value lube oil stock and fuel products. The catalyst comprises: a porous amorphous matrix consisting of alumina-silica-titania polygels, a hydrogenation component consisting of combinations of nickel-molybdenum or nickel-tungsten metals and a crystalline alumino silicate of the ZSM-series in the ammonium or the protonic form. A second catalyst is disposed downstream of a reaction zone in which the feed is contacted under hydroprocessing conditions with an active hydrodenitrogenation function. The hydrodenitrogenation catalyst contains an inorganic matrix oxide consisting of alumina, silica, magnesia or a mixture thereof, and at least one hydrogenation component selected from the Group VIB and Group VIII elements, and a silicaceous molecular sieve component substantially in the ammonium or hydrogen form.
U.S. Pat. No. 3,016,346 to O'Hara describes a nickel-molybdenum catalyst supported on alumina and a smaller amount of titania (0.5 to 5.0% by weight). The catalyst contains molybdenum, cobalt and nickel. The catalyst has hydrodenitrogenation activity and also inhibits those hydrocracking reactions which result in excessive coke deposits on the catalysts when the catalyst is used for hydrotreating a thermally cracked middle fraction in a standard relative activity test. The alumina-titania support in O'Hara is prepared by co-precipitation of aluminum and titanium hydroxides from a solution of titanium tetrachloride, an aqueous ammonium hydroxide solution and aluminum chloride, and contains 3.7% by weight of titanium.
U.S. Pat. No. 4,465,790 to Quayle discloses a hydrodenitrogenation catalyst comprising catalytic molybdenum and nickel on a co-precipitated support of alumina and titania. The support is co-precipitated from solutions of the sulfates of aluminum and titanium. Titania in the support constitutes more than 5% by weight of the catalyst. The resulting hydrogel is processed using standard techniques to form a catalyst support. Catalytic metals are then impregnated onto the support. However, this particular catalyst has relatively poor mechanical properties and is difficult to extrude during manufacture.
European Patent Application 0 199 399 discloses a method for making a hydrocarbon conversion catalyst with improved hydrodesulfurization and hydrodenitrogenation activity. The catalyst contains a Group VI-B metal that is either molybdenum or tungsten and a Group VIII metal that is either cobalt or nickel that are incorporated into a titania-containing alumina support. The catalyst is prepared by mulling together alpha aluminum monohydrate and titanium dioxide at a molar ratio of Al.sub.2 O.sub.3 :TiO.sub.2 ranging from 3:1 to 5:1, acetic acid in a concentration ranging from 2.5 to 3.5 parts of acid per 100 parts of Al.sub.2 O.sub.3 by weight, and sufficient water to produce an extrudable mixture. The mixture is then extruded and calcined. The metals are impregnated onto the support by conventional methods.